As for soil treatment for improving a soft foundation of a ground into a strong and solid one, for example, it has been known well known in the art to consolidate the constituent sand and soil of the foundation by the use of cement or a similar soil construction modifier. More specifically, generally a geotechnological engineering method of this sort includes the steps of excavating foundational sand and soil of a ground, adding and mixing a soil improving material uniformly into excavated soil and sand, refilling the excavated ground with improved soil, and finally compacting the refilled ground. For carrying out such a foundational soil treatment, there have to be provided various equipments including means for excavating foundational sand and soil of a ground, means for feeding a soil improving material, means for mixing soil improving material uniformly with excavated sand and soil, and means for refilling and compacting the ground.
For a soil treating operation as mentioned above, at least an excavation machine like a hydraulic power shovel is inevitably required. In this regard, a hydraulic power shovel is generally resorted to as an excavation means. In case of a vehicular or traveling type power shovel, the base carrier is provided with either a crawler or wheel type vehicle drive mechanism. As a vehicle drive, it is preferable for the hydraulic power shovel to have a crawler type drive mechanism, taking into consideration the conditions of the grounds which in many cases have rough and soft surfaces, and at the same time from the standpoint of securing stability of the vehicle body under inferior travel conditions or against large excavational resistance forces.
On the other hand, for producing soil of improved construction or properties by uniformly mixing excavated sand and soil with a soil improving material, there have been known a number of methods, which can be largely categorized into a method of mixing a soil improving material with sand and soil by the use of a mixer machine, and a sprinkling method or a method of sprinkling an additive soil improving material over excavated sand and soil as the latter is turned over by an excavator.
As for the mixer machine, it should be at least equipped with a mixing tank with a soil mixing mechanism and an additive feed mechanism. Excavated sand and soil can be fed to a mixing tank directly by and from a hydraulic power shovel which is used for excavation of sand and soil. However, due to varying positional relations in operation between a mixer machine and a hydraulic power shovel, it has been the general practice to pile up excavated sand and soil in a predetermined depository place which is convenient for transfer to a mixer machine. In this connection, for example, there has been known a mixing machine as disclosed in Japanese Patent Publication H1-49538 (i.e., B2 publication), which is in the form of a traveling type mixing machine having, on a wheel type base carrier, a soil feed mechanism with a bucket for transferring sand and soil from a depository place with a heap of sand and soil which has been excavated beforehand by the use of a hydraulic power shovel or the like, along with a mixing tank and an additive feed section. The soil feed mechanism is horizontally rotatable within a limited angle relative to a vehicle body. A fixed amount of excavated sand and soil is thrown into the mixing tank along with a fixed amount of soil improving material and mixed together by a mixing means to produce improved soil batchwise. Improved soil of each batch is discharged from the mixing tank at a predetermined place.
In the case of the above-described conventional soil treating system using a traveling type mixing machine, it is inevitably necessitated to excavate sand and soil beforehand by the use of a hydraulic power shovel or the like. This traveling type mixing machine is provided with a soil feed mechanism with a bucket which, however, is difficult to use directly for excavation of a ground, partly because the wheel type base carrier is not suitable for travels on soft and hazardous ground surfaces at ground working sites and partly because the soil feed mechanism can rotate in the horizontal direction only in a limited angle range to limit the position of ground excavation by the machine. In addition to incapability of ensuring stability of the vehicle against large excavational resistance. It follows that sand and soil has to be excavated separately by the use of a hydraulic power shovel or the like and heaped up at a depository place which is accessible by the traveling mixing machine, resulting in an increased number of working steps. Besides, the batchwise soil treatment by a mixer tank is unsatisfactorily inferior in throughput capacity.
In contrast, in the case of the method of sprinkling additive soil improving material over a ground as mentioned above, firstly soil improving material is sprinkled over a ground which needs improvements to its foundation, and then the ground is excavated in such a manner as to mix soil improving material with sand and soil as the latter is dug out and turned over by an excavation means. In this instance, for mixing soil improving material into sand and soil being excavated, it is conceivable to use an excavation machine with a bucket like a hydraulic power shovel. However, without meticulous skills, it is difficult to mix a soil improving material uniformly into excavated sand and soil in a broad working area by the use of an excavating machine of this sort. In this connection, Japanese Laid-Open Utility Model Specification S56-733 discloses a machine with excavating and mixing means. According to this laid-open Utility Model Specification, the excavating and mixing means is constructed in the form of a rotor with a large number of radial cutter blades connected to a rotational shaft, as an attachment to a front working mechanism of a hydraulic power shovel. This excavating and mixing rotor is mounted on a distal end of an arm which is connected to a boom of the hydraulic power shovel. While the hydraulic power shovel is driven to travel along a ground surface, the rotational shaft of the excavating and mixing rotor is put in rotation and its rotating cutter blades are pushed against the ground surface through operations of the boom and arm of the hydraulic power shovel, and at the same time a soil improving material is sprinkled over and mixed with sand and soil being dug up by the rotor blades.
A soil treating system using an excavating and mixing means, which can excavate and treat soil continuously as described above without necessitating to heap up excavated sand and soil at one depository place beforehand, has a higher soil processing capacity. However, such a system has an inherent problem in that the sprinkling of soil improving material could pose adverse effects on the environment, in addition to the problem of loud noises which are produced by the rotor in such a level as would invite prohibition of its use in or in the neighborhood of densely populated areas. Besides, the depth of excavation by the rotor depends on the length of its cutter blades. Currently available cutter blades are limited to a length of about 1 meter at the longest and therefore not suitable for application to foundational soil treatments involving deep excavations.
Further, for fortifying foundational soil construction of a ground, it is necessary to mix a soil improving material with excavated sand and soil uniformly in a predetermined mixing ratio. This is because it is probable that, after construction of a building on a treated ground, the foundation will sink down irregularly if the mixing ratio is varied from one place to another. A foundation of a ground can be fortified to a sufficient degree despite irregular variations in mixing ratio if a soil improving material is used in a wastefully large mixing ratio at the sacrifice of considerable increases in cost. In the case of the soil treatment using a mixing tank, it is possible to mix a soil improving material substantially uniformly with excavated sand and soil but the mixing operation takes a great deal of time. In addition, for controlling the mixing ratio, it becomes necessary to provide metering means on a mixing tank to measure the amount of charging sand and soil, and to control the feed rate of a soil improving material according to a predetermined mixing ratio. For the control of mixing ratio, the soil treating process will further require a longer operational time for each batch.
In the case of the soil treatment using a rotor type excavating and mixing means as mentioned above, it is extremely difficult to sprinkle a soil improving material uniformly over the entire sand and soil being excavated by the rotor, namely, it is difficult to suppress irregular variations in mixing ratio or rate to such a degree as to preclude the problem of non-uniform sinking which might occur to the foundation of a ground under the weight of a building or other structures.